LT#2: Determining and Communicating ∆H

Question 1

What is a calorimeter?

Answer 1

A piece of lab equipment that insulates a system so that the energy lost or gained can be measured.

Calorimeters surround the system with water, which we can easily track the temperature change of using a thermometer.

Question 2

How do you calculate the ∆H of a reaction using a calorimeter?

Answer 2

1. Calculate the amount of heat the water in calorimeter absorbs/releases using Qw=mc∆T.
2. Change Qw into Qrxn by flipping sign (∆Esystem = -∆Esurroundings).
3. Calculate enthalpy change using ∆H = ∆Esystem/mol of the limiting reactant.

Question 3

What assumptions need to be made when performing calorimeter calculations?

Answer 3

1. That the volume of water is equal to the volume of the liquid in the calorimeter.
2. That the water in the calorimeter is pure so that it has a c value of 4.18.
3. That the water is the only thing that exchanges energy with the system.
4. That no energy is lost from the calorimeter.

Question 4

How are the errors involved in calorimeter calculations minimized?

Answer 4

Error from assumption 1 and 2 is minimized by using only dilute solutions (1 M max).

Error from assumption 3 and 4 is minimized by the materials used and design of your calorimeter.

Question 5

What are the limitations of coffee cup calorimeters?

Answer 5

1. We can only do reactions that can occur in water.
2. We can only do reactions that don’t produce too much heat to melt the cup.
3. We can only do reactions with chemicals that don’t react with the cup.